1. Field of the Invention
The present general inventive concept relates to a method and apparatus to drive an image display device, and more particularly, to a method and apparatus of compensating for a kick-back voltage to reduce generation of flicker in a liquid crystal display (LCD).
2. Description of the Related Art
A conventional kick-back compensation circuit is disclosed in Korean Patent No. 2006-062645 and Japanese Patent No. 2001-128090.
A liquid crystal display (LCD) displays images by controlling light transmissivity of a liquid crystal element using an electric field. The LCD includes an LCD panel on which liquid crystal cells are arranged in a matrix and a circuit for driving the LCD panel.
Referring to FIG. 1, a gate line GL and a data line DL intersect each other on a lower glass of the LCD panel and a thin film transistor TFT for driving a liquid crystal cell LC is arranged at the intersection of the gate line GL and the data line DL. In addition, a storage capacitor Cst for maintaining the voltage of the liquid crystal cell LC is connected in parallel with the liquid crystal cell LC. The liquid crystal cell LC includes a pixel electrode 11 and a common electrode 12. A capacitor Cgd is connected between the gate line G1 and the liquid crystal cell LC, that is, a gate and a drain of the TFT.
When voltages having the same polarity are continuously applied to liquid crystal cells, displayed images are deteriorated. To prevent this, an AC data voltage having a periodically inverted polarity is used to drive the liquid crystal cells. The polarity of the AC data voltage is inverted for each frame on a basis of a voltage Vcom applied to a common electrode 12.
When the gate voltage of a thin film transistor is logic high, a liquid crystal cell corresponding to the thin film transistor is charged up to the data voltage. However, the voltage charged in the liquid crystal cell is distorted by a kick-back voltage according to a parasitic capacitance of the thin film transistor at the instant of time when the gate voltage of the thin film transistor is transited to logic low, as illustrated in FIG. 2. FIG. 2 illustrates that an RMS (Root Mean Square) value difference between a positive pixel data voltage and a negative pixel data voltage is generated due to the kick-back voltage, which generates flicker. The kick-back voltage varies according to positions in a relatively large display device.
To compensate for the flicker caused by the kick-back voltage, the voltage Vcom applied to the common electrode is controlled using a passive element such as a variable resistor. However, the kick-back voltage varies according to positions in an LCD panel due to RC delay in gate lines, and thus an operation of correcting common voltages for the respective positions using a large number of passive elements is required. Furthermore, it is difficult to accurately control the common voltages with a manual operation.